Abstract: The knowledge of the dynamics of engine working load is essential condition for dynamic analyzing and matching for engine and tractors. In this paper, according to the statistical examination of the experimental data in field and laboratory test, the fundamental statistical properties of working load of engine in plowing and rototilling are summarized. The working load of engine in plowing can be taken for stable and normal random load whose power spectrum peak value is below 2 Hz. The working load of engine in rototilling contains both periodic element whose fundamental frequency is rotating speed of the blade shaft and normal random load of which the parts of energy centers in fundamental frequency and others are distributed over wider frequency band. In frequent speed the power spectrum of the engine load in plowing and the low random element of the engine load in rototilling can be simulated by a single peak spectrum function.